This invention relates to the delivery of radioisotopes to a disease-causing pathogen using a pathogen-targeting material conjugated to the radioisotope.
It is known to deliver cytotoxic radioisotopes to the nucleus of a tumor cell using a targeting protein or polypeptide conjugated with a radio-labeled nucleic acid-targeting small molecule. See, for example, U.S. Pat. No. 5,759,514. However, the use of radio-isotopes to seek and destroy disease-causing living pathogens such as bacteria or viruses has not heretofore been suggested.
Some strains of bacteria and viruses are very resistant to conventional drug therapy and are capable of killing or seriously debilitating the patient. Some strains are capable of mutating into a predominantly drug resistant form during the course of drug treatment, resulting in the death or debilitation of the patient. The widespread use of a particular drug treatment furthermore favors the genetic selection of strains which are resistant to that particular course of treatment. The presence of drug resistant strains of bacteria and viruses poses a growing world wide health threat.
A method for treating patients which have been infected with a drug-resistant pathogen would be very desirable.
In one embodiment of the invention, there is provided a composition of matter comprising a living pathogen-targeting organic moiety which is conjugated to a radioisotope which has a half-life of less than 100 days.
A preferred embodiment of the composition of matter can be synthesized by bringing together a radioisotope having a half life of less than 100 days with a greater than a stoichiometric amount of a complexing agent so as to form a first mixture containing a reaction product between the radioisotope and the complexing agent; removing the excess complexing agent from the mixture; and bringing together the first reaction product and an antibody substance so as to form a second mixture containing a reaction product between the first reaction product and the antibody substance.
The invention also provides a method for treating an infectious disease caused by living pathogens. Antibodies produced in response to the pathogens are obtained and replicated. The replicated antibodies are conjugated with a radioisotope which has a half-life of less than 100 days to produce a therapeutic composition. The therapeutic composition is then administered in a manner to bring the therapeutic composition into contact with the living pathogens.
Another method in accordance with the invention for treating an infectious disease caused by living pathogens is carried out by identifying the pathogens causing the infectious disease, selecting a therapeutic composition comprising an organic moiety which is chemically selective for attachment to the pathogens and which is conjugated to a radioisotope which has a half-life of less than 100 days, and administering the therapeutic composition in a manner so that the therapeutic composition becomes attached to the pathogens.
In one embodiment of the invention, there is provided a composition of matter comprising a living pathogen-targeting organic moiety which is conjugated to a radioisotope which has a half-life of less than 100 days.
Recent evidence has shown that radioisotopes which emit alpha, beta, or gamma radiation, and especially those of fairly short half-life and which emit Auger electrons during the decay process may be useful for inducing receptor cell specific cytotoxicity.
When a radioisotope decays by orbital electron capture or internal conversion, inner atomic shell vacancies are created in the residual atom. This highly excited atom attains a stable electronic configuration rapidly in a time scale of about 10xe2x88x9215 seconds via radioactive and non-radioactive transitions. In general, Auger, Coster-Kronig and super Coster-Kronig processes dominate the atomic vacancy cascades. As a result, numerous electrons are ejected from the atom and most of these Auger electrons have very low kinetic energies (about 20-500 eV) with extremely short ranges (a few nanometers) in water. Even though the energy carried by each of these electrons is only a small fraction of the total energy released in the decay process, their collective energy deposition is extremely high. Hence when the decays occur in the immediate vicinity of the critical biological molecules such as DNA, intracellular transmitters or any of the apoptotic cascade mechanisms, the biological effects to that cell are expected to be devastating.
Usually, radioisotopes used in accordance with the invention will have a half-life in the range of from about 1 to about 10 days. Preferably, the radioisotopes emit Auger electrons. Examples of suitable radioisotopes are Phosphorus 32, Copper 67, Gallium 67, Bromine 77, Yttrium 90, Technetium 99, Indium 111, Iodine 125, Iodine 131, Rhenium 186, Rhenium 188, Platinum 195, Bismuth 213, and Astatine 225. Of these, Copper 67, Yttrium 90, Indium 111, Rhenium 186, and Platinum 195 are preferred because these radioisotopes have distinct cytotoxic properties which may be exploited for therapy by the biologically directed targeting. In particular, antibodies labeled with DOTA derivatives incorporating Yttrium 90 and Indium 111 have shown excellent kinetic stability under physiological conditions. Of these two, Indium 111 is most preferred, because of relatively low toxicity to man as compared to Yttrium 90.
Compounds that are labeled with Auger electron emitters are most effective when the compound is internalized within or attached to the cell in a manner capable of activating apoptosis. Auger electrons provide very high-energy emissions but do so over a very short distance or action, which is less than 1-20 microns. This allows for an Auger emitting radioisotope to bring a high energy destructive force into areas to cause critical DNA strand damage (mitochondrial or nuclear). This, in turn activates the mechanism of apoptosis. Therefore, for a radioisotope-ligand to be a particularly desirable therapeutic agent, the compound must have a high cell to be destroyed-to background tissue ratio, a high therapeutic ratio and pharmacokinetic biodistribution profiles that optimize receptor binding, ligand internalization and cellular retention. The effects, therefore, of Auger electron emitters depend upon their cellular and sub-cellular location, which is governed, in turn, by the chemical form of the molecular agent (bioactive substance) to which the radioisotope has been attached.
Generally speaking, the living pathogen-targeting organic moiety is in the form of an antiviral, antifungal or an antibacterial antibody, although fragments of such antibodies or antibiotics which function to selectively carry the radioisotope into or onto a targeted pathogen are also considered suitable. Viruses, fungi, bacteria, or prions may be selected as targets by appropriate selection of the organic moiety. Usually, the organic moiety has a surface chemistry which associates with a surface chemistry of the targeted pathogen.
More preferably, the organic moiety has a surface chemistry to associate with a unique surface chemistry of the targeted pathogen.
Circulating antibodies normally recognize an antigen in the serum or tissue fluids and, furthermore, there are five identifiable classes: IgG, IgA, IgM, IgD and IgE. In addition to antigen binding, all antibodies exert other specific biological activities. The antigen-binding site is usually one in which there is a Fc fragment and two-antigen binding FAB fragments. X-ray crystallography and electron microscopy has provided the structural and biochemical organization of these moieties. Disulfide bonds predominate in cross-linking many of these domains. The primary function of any antibody is to bind any recognizable antigen. Recently, libraries of human specific antibody variable genes have been constructed for recombinant filamentous phages, which display the antibodies on their surface, and it is possible to select from high affinity antibodies for any chosen cell surface antigens from these libraries.
Phage antibodies that bind to a particular antigen may be separated from non-binding phage antibodies by antigen selection and the bound antibodies are recovered by elution. Repeated rounds of selection can isolate antigen-binding phages that were present at the start of the process at frequencies of less than one in a billion.
One technique of producing a homologous population of antibodies of known antigen specificity, are known as hybridomas that are derived from a single B cells and are called monoclonal antibodies. Another technique for producing antibody molecules is named phage antibody or phage libraries. In this case, gene segments encoding antigen-binding variable or V domains of antibodies are fused to genes encoding the coat protein of a bacteriophage. A collection of recombinant phage, each displaying a different antigen-binding domain on its surface is known as a phage display library. Each phage isolated in this way will produce a monoclonal antigen-binding particle analogous to a monoclonal antibody. Genes encoding the antigen-binding site, which are unique to each phage, can then be recovered from the phage DNA and used to construct genes for a complete antibody molecule by joining them to gene segments that encode the invariant parts of an antibody. When these reconstructed antibody genes are introduced into a suitable host cell line, the transferred cells secrete antibodies with all of the desirable characteristics on monoclonal antibodies that are produced from hybridomas.
The antibody binds stably to its antigen as the antibodies recognize the surface features of the native folded protein antigen and the antibody molecules can thus be used to locate their target molecules accurately in single cells or in tissue sections.